Auto-adjusting system for an optical incident angle

ABSTRACT

An auto-adjusting system for an optical incident angle comprises a memory, a linear tilt calculation unit, a non-linear tilt calculation unit, a controller, and a tilt actuator. The memory is used for storing a linear tilt compensation table and a non-linear tilt compensation table. The linear tilt calculation unit is used for calculating the corresponding linear tilt dac value by consulting the linear tilt compensation table according to a first radius and a focus output voltage. According to a predetermined comparison procedure, the non-linear tilt calculation unit is used for generating a second radius wherein the compact disc begins to generate non-linear deformation and then obtaining the corresponding non-linear tilt compensation parameter by consulting the non-linear tilt compensation table according to the first radius and the second radius. The controller is used for controlling the pickup head, the memory, the linear tilt calculation unit, and the non-linear tilt calculation unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an auto-adjusting system for an opticalincident angle, especially to an auto-adjusting system for an opticalincident angle applied in an optical information recording/reproducingapparatus, which is used for correcting the inclination of the pickuphead on line, so that the laser beam can be kept in a predeterminedoptical incident angle to read data from the compact disc.

2. Description of the Prior Art

This era is the time of information explosion. As the amount of dataincreases quickly, the technology of information storage and process isalso improving rapidly. The technology of optical information storage isquite important in the related field.

In order to improve the technology of information storage and increasethe amount of information storage, the relative technology of opticalinformation recording/reproducing apparatus is developed mainly byspeeding up the rotation speed of compact discs and adopting the laserbeams with shorter wavelengths. On one hand, the rotation speed ofcompact disc is increasing day by day; on the other hand, the technologyof laser beam is improved from the standard of CD (wavelength is about780 nm) to the standard of DVD (wavelength is about 650 nm), or evenlaser with shorter wavelengths, e.g. blue ray. However, how to maintainthe optical information recording/reproducing quality is always theproblem that needs to be overcome. Therefore, many kinds of technologyof servo control are invented.

In the prior art, the technologies of servo control applied in theoptical information recording/reproducing apparatus comprise spindleservo, focus servo, tracking servo, and seek servo. Theseclassifications and the functions of all kinds of servo technologies arewell-known to those skilled in the art and can be carried out on acontroller chip with DSP as the core. The relative technology of thepresent invention is more about focus servo. The focus servo is used forcontrolling the pickup head to move in the direction vertical to thecompact disc, so that a focus distance is kept between the pickup headand the compact disc. Furthermore, the focus servo can receive the focuserror signal (FE signal) reflected from the compact disc and output afocus output voltage (FOSO or FOO) to control the pickup head, so thatthe FE signal is close to zero. Therefore, the pickup head can stillfocus on the appropriate position of the compact disc while it ismoving. There are many reasons why the pickup head cannot maintain afocus distance with the compact disc; for example, the compact disc isnot smooth, or the compact disc wobbles or is deformed while rotating.Under the above conditions, the pickup head must move in a verticaldirection to maintain the focus distance with the compact disc. However,as the wavelength of laser beam reduces and the rotation speed ofcompact disc increases, only maintaining the focus distance between thepickup head and the compact disc automatically is still not enough tokeep a consistent quality for the optical informationrecording/reproducing system.

The reason that leads to the above disadvantages of the prior art is dueto the fact that the laser beam cannot be orthogonal to the compact discwhile the laser beam is focused on the compact disc. In the process ofdesigning the optical information recording/reproducing apparatus, theabove condition is not part of the consideration; only the offset offocus distance caused by wobbling or deformation, while the compact discrotates, is being considered. In other words, although the technology offocus servo enables the pickup head to maintain the focus distance withthe compact disc, whether the laser beam is orthogonal to the compactdisc cannot be guaranteed. Therefore, the quality of the obtained signalwill be lowered.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of the relativeposition between an optical information recording/reproducing apparatus10 and an optical disc 14 of the prior art. The optical informationrecording/reproducing apparatus 10 of the prior art comprises a rotationdevice 12, a pickup head track 16, and a pickup head 18. The rotationdevice 12, the compact disc 14, the pickup head track 16, and the pickuphead 18 respectively have an adjustable inclination device to adjust thecorresponding inclination of a spindle 22, a disc spindle 24, a pickuphead track spindle 26, and a mirror spindle 28. Taking the rotationdevice 12 as an example, three inclination adjusting screws 29 are setthereon. If the spindle 22, the disc spindle 24, the pickup head trackspindle 26, or the mirror spindle 28 is corrected inappropriately or istilted, a laser beam 30 outputted by the pickup head 18 to the compactdisc 14 will not be able to generate an orthogonal incidence (90degree).

Please refer to FIG. 1 and FIG. 2. FIG. 2 is a schematic diagram of alaser beam 30 inputted to a compact disc 14 shown in FIG. 1. As shown inFIG. 2, the compact disc 14 comprises a plurality of different recordingblocks 32. As shown in FIG. 1, the optical informationrecording/reproducing apparatus 10 may enable the pickup head 18 and thecompact disc 14 to maintain a focus distance w1 by the focus servo ofthe prior art. Also, the laser beam 30 can focus on the specificrecording block 32 correctly by cooperating with the tracking servo ofthe prior art. However, as shown in FIG. 2, the prior art cannot detectand adjust an inclination θ1 resulted from the laser beam that is notorthogonal. This disadvantage causes lower signal quality while readingor recording the optical information.

Besides the tilt of spindle 22, disc spindle 24, pickup head trackspindle 26, and mirror spindle 28 shown in FIG. 1, there is anotherreason that causes the inclination θ1; that is, the compact disc 14 isnot a smooth but a tilt one.

The inclination θ1 caused by the tilt of spindle 22, disc spindle 24,pickup head track spindle 26, and mirror spindle 28 does not change whenthe distance between the recording block 32 and the compact disc 14 isdifferent. The inclination θ1 is called linear inclination.

On the other hand, because of the different distance between therecorded/reproduced recording block and the center of the compact disc14, the inclination caused by the tilt compact disc is different.Therefore, this inclination is called non-linear tilt. The position fromthe center along the radius to where a tilt is generated is callednon-linear deformation.

There are presently a few research projects aiming at the problem of theincident angle between the laser beam and the compact disc. Most of theresearch needs a tilt sensor for detecting the offset of the incidentangle between the laser beam and the compact disc. According to thedetection result the pickup head is adjusted, and the laser beam may becorrected to be orthogonal to the compact disc. However, theinstallation of the tilt sensor will increase the cost of production.Therefore, there are only a few optical informationrecording/reproducing apparatus which currently has the tilt sensorinstalled.

For this reason, the prior art lacks an auto-adjusting system for anoptical incident angle and an auto-adjusting system for an opticalincident angle without the tilt sensor, so as to be acceptable under theconsideration of cost when producing the optical informationrecording/reproducing apparatus.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide an auto-adjustingsystem for an optical incident angle applied in an optical informationrecording/reproducing apparatus, which is used for correcting theinclination of the pickup head on line, so that the laser beam can bekept in a predetermined optical incident angle to read data from thecompact disc, and thus maintaining the optical informationrecording/reproducing quality.

The other objective of the present invention is to provide anauto-adjusting system for an optical incident angle without a tiltsensor, so as to be acceptable under the consideration of cost whenproducing the optical information recording/reproducing apparatus.

The present invention provides an auto-adjusting system for an opticalincident angle applied in optical information recording/reproducingapparatus. The above optical information recording/reproducing apparatuscomprises a pickup head and a tilt actuator. The pickup head generates alaser beam to read data from a recording block of a first radius on acompact disc and receive a focus output voltage from the focus servo(e.g. the focus output voltage may be provided by the focus servo withinthe controller). The tilt actuator outputs a tilt adjusting signal tocorrect the inclination of the pickup head, so as to keep the laser beamat a predetermined optical incident angle to read data from the compactdisc.

The auto-adjusting system for an optical incident angle comprises amemory, a linear tilt calculation unit, a non-linear tilt calculationunit, and a controller. The memory is used for storing a linear tiltcompensation table and a non-linear tilt compensation table. The lineartilt compensation table is built via a predetermined linear tiltadjusting procedure and comprises a plurality of focus output voltagesand a plurality of corresponding linear tilt dac values. The non-lineartilt compensation table records a plurality of non-linear tiltcompensation parameters. Each non-linear tilt compensation parameter isa function of the first radius and a second radius, wherein the compactdisc begins to generate non-linear deformation. The linear tiltcalculation unit is used for calculating the corresponding linear tiltdac value by consulting the linear tilt compensation table according tothe first radius and the focus output voltage. According to apredetermined comparison procedure, the non-linear tilt calculation unitis used for generating the second radius, wherein the compact discbegins to generate non-linear deformation, and then obtaining thecorresponding non-linear tilt compensation parameter by consulting thenon-linear tilt compensation table according to the first radius and thesecond radius. The controller is used for controlling the pickup head,the memory, the linear tilt calculation unit, and the non-linear tiltcalculation unit. Wherein the pickup head reads data from the recordingblock on the compact disc, the controller controls the calculation of atilt compensation equation by inputting the linear tilt dac valuegenerated by the linear tilt calculation unit and the non-linear tiltcompensation parameter generated by the non-linear tilt calculationunit. The controller also enables the tilt actuator to output thecorresponding tilt adjusting signal to the pickup head according to thecalculation result, so as to adjust the inclination of the pickup headon-line.

Compared with the prior art, the optical informationrecording/reproducing apparatus doesn't need to install a tilt sensor;it obtains the tilt of the optical incident angle from the laser beam tothe compact disc as in the prior art, which utilizes the focus outputvoltage to keep a focus distance between the pickup head and the compactdisc. After calculating and obtaining the tilt of the optical incidentangle, the auto-adjusting system for an optical incident angle of thepresent invention further actuates the inclination of the pickup head,so that the laser beam is parallel to the normal direction of theselected recording block, thus achieving the objective of auto-adjustingfor an optical incident angle. Therefore, the optical informationrecording/reproducing apparatus, which utilizes the auto-adjustingsystem for an optical incident angle of the present invention, not onlycan maintain the optical information recording/reproducing quality butis also acceptable under the consideration of cost when producing theoptical information recording/reproducing apparatus.

The advantage and spirit of the invention may be understood by thefollowing recitations together with the appended drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 is a schematic diagram of the relative position between anoptical information recording/reproducing apparatus and an optical discof the prior art.

FIG. 2 is a schematic diagram of a laser beam inputted to a compact discshown in FIG. 1.

FIG. 3 is a schematic diagram of an optical informationrecording/reproducing apparatus according to the present invention.

FIG. 4A is a schematic diagram of inclination 0 of the compact disc inthe optical information recording/reproducing apparatus shown in FIG. 3.

FIG. 4B is a schematic diagram of inclination φ1 of the compact disc inthe optical information recording/reproducing apparatus shown in FIG. 3.FIG. 4C is a schematic diagram of inclination φ2 of the compact disc inthe optical information recording/reproducing apparatus shown in FIG. 3.

FIG. 5 is a flowchart of building the tilt dac values of the linear tiltcompensation table shown in FIG. 3.

FIG. 6 is a schematic diagram of a tilt compact disc used by the opticalinformation recording/reproducing apparatus shown in FIG. 3.

FIG. 7 is a flowchart of comparison procedure of generating secondradius distance r₀ as shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an auto-adjusting system for an opticalincident angle in an optical information recording/reproducingapparatus. The optical information recording/reproducing apparatus ofthe present invention is able to do away with the use of the tilt sensorof the prior art and can still obtain the optical incident angle toauto-adjust the pickup head, so as to substantially keep the pickup headwith the compact disc at the orthogonal position of 90 degree.

Please refer to FIG. 3. FIG. 3 is a schematic diagram of an opticalinformation recording/reproducing apparatus 40 according to the presentinvention. The optical information recording/reproducing apparatus 40comprises a pickup head 42, a pickup head guiding track 43, anauto-adjusting system 44 for an optical incident angle, and a tiltactuator 46. The pickup head 42 generates a laser beam 48 to read datafrom a recording block 52 of a first radius r on a compact disc 50 andreceives a focus output voltage (FOSO) 54 of the focus servo inresponsive to the reflected laser beam 48. The tilt actuator 46 outputsa tilt adjusting signal 56 to correct the inclination of the pickup head42, so as to keep the laser beam 48 at a predetermined optical incidentangle to read data from the compact disc 50.

The pickup head 42 comprises a laser diode for generating the laser beam48 and a photo detector for detecting the laser beam 48 reflected fromthe recording block.

The compact disc 50 comprises recording blocks. The pickup head track 43is used for enabling the pickup head 42 to move in parallel to theradial direction of the compact disc 50, in order to read data fromrecording blocks, which include the recording block 52 with the firstradius distance r. The starting position 55 represents the innermostposition, which can be used to record/reproduce data, of the compactdisc 50.

The optical information recording/reproducing apparatus 40 comprises aspindle 57 for rotating the compact disc 50. There is at least oneinclination adjusting screw accommodated on the spindle 57. In thisembodiment, there are three inclination adjusting screws 59 accommodatedon the spindle 57. The inclination adjusting screws 59 can adjust theinclination of the shaft 58 of the spindle 57 and the horizontalinclination as the compact disc 50 rotates. The function of the threeinclination adjusting screws 59 is similar to the inclination adjustingscrew 29 of the prior art shown in FIG. 1.

The auto-adjusting system 44 for an optical incident angle of thepresent invention comprises a memory 58, a linear tilt calculation unit60, a non-linear tilt calculation unit 62, and a controller 64. Thememory is used for storing a linear tilt compensation table 66 and anon-linear tilt compensation table 68.

The linear tilt compensation table 66 is built via a predeterminedlinear tilt adjusting procedure and comprises a plurality of focusoutput voltages and a plurality of corresponding linear tilt dac values.The non-linear tilt compensation table 68 records a plurality ofnon-linear tilt compensation parameters. Each non-linear tiltcompensation parameter is a function of the first radius r and a secondradius r₀ wherein the compact disc 50 begins to generate non-lineardeformation.

The linear tilt calculation unit 60 is used for calculating thecorresponding linear tilt dac value 70 by consulting the linear tiltcompensation table 66 according to the first radius r and the focusoutput voltage 54 provided by the focus servo.

The non-linear tilt calculation unit 62 is used for generating thesecond radius r₀, wherein the compact disc 50 begins to generatenon-linear deformation according to a predetermined comparisonprocedure, and then obtaining the corresponding non-linear tiltcompensation parameter 72 by consulting the non-linear tilt compensationtable 68 according to the first radius r and the second radius r₀.

The controller 64 is used for controlling the pickup head 42, the memory58, the linear tilt calculation unit 60, and the non-linear tiltcalculation unit 62.

When the pickup head 42 reads data from the recording block 52 on thecompact disc 50, the controller 64 controls the calculation of a tiltcompensation equation by inputting the linear tilt dac value 70generated by the linear tilt calculation unit 60 and the non-linear tiltcompensation parameter 72 generated by the non-linear tilt calculationunit 62. The controller 64 also enables the tilt actuator 46 to outputthe corresponding tilt adjusting signal 56 to the pickup head 42according to the calculation result 53, so as to adjust the inclinationof the pickup head 42 on-line when the pickup head moves and worksnormally (e.g. when the pickup head moves along the top of the compactdisc to read data from the compact disc). Taking this embodiment as anexample, the controller 64 adjusts the inclination of the pickup head 42every 200 ms to 500 ms on line.

The controller 64 generates the calculation result 53, defined as Theta,from the following tilt compensation equation:

Theta = b LinearTiltDAC + (bLinarTiltDAC − bTiltDAC_offset) + 2 * β(bLinarTiltDAC − bTiltDAC_offset);

In the above equation, the linear tilt dac value 70 calculated by thelinear tilt calculation unit 60 is defined as bLinearTiltDAC. The lineartilt dac value obtained by the pickup head 42 when reading the startposition 55 of the compact disc 50 is defined as bTiltDAC_offset. Thenon-linear tilt compensation parameter 72 obtained by the non-lineartilt calculation unit 62 is defined as β.

The tilt actuator 46 comprises a digital to analog (D/A) converter 49for converting the calculation result 53 of the controller 64 into thecorresponding tilt adjusting signal 56 to adjust the inclination of thepickup head 42. The tilt actuator 46 enables the laser beam 48,generated by the pickup head 42, to parallel the normal direction of theselected recording block 52, so that the optical incident angle issubstantially kept at 90 degree to reduce the error rate when readingdata from the recording block 52. In this embodiment, the frequency thatthe controller 64 adjusts the inclination of the pickup head 42 on lineis once per 200 ms to 500 ms.

As the above description, the linear tilt adjusting procedure used tobuild the linear tilt compensation table 66 utilizes a standard non-tiltdisk, so that the linear tilt adjusting procedure is not affected bynon-linear deformation or non-linear tilt that are caused by the tiltcompact disc. The linear tilt adjusting procedure builds the linear tiltcompensation table by the following steps: place a normal non-tilt diskin the optical information recording/reproducing apparatus 40, adjustthe inclination adjusting screw of the spindle 57 to enable the normalnon-tilt disk to rotate under different inclination, record thecorresponding focus output voltages 54 in several different radiuspositions under each inclination angle, and obtain the correspondinglinear tilt dac values to complete the linear tilt compensation table66.

Please refer to FIG. 4A to FIG. 4C. FIG. 4A is a schematic diagram ofinclination 0 of the compact disc 50 in the optical informationrecording/reproducing apparatus 40 shown in FIG. 3. FIG. 4B is aschematic diagram of inclination φ1 of the compact disc 50 in theoptical information recording/reproducing apparatus 40 shown in FIG. 3.FIG. 4C is a schematic diagram of inclination φ2 of the compact disc 50in the optical information recording/reproducing apparatus 40 shown inFIG. 3. The following description will describe the method for buildingthe linear tilt compensation table 66 shown in FIG. 3 by the above threediagrams. If more tilts with different inclination are selected, thelinear tilt compensation 66 will be more accurate. For the convenienceof description, this embodiment only takes the above three diagrams asexamples. The tilt adjusting screw 59 of the spindle 57 may be adjustedto enable the compact disc 50 to rotate at different inclination 0, φ1,and φ2, as shown in FIG. 4A, FIG. 4B, and FIG. 4C respectively.

As shown in FIG. 4A, FIG. 4B, and FIG. 4C, the pick up head 42 receivescorresponding focus output voltages 54, that are obtained afterfiltration via a low-pass filter 65, at different radius distances, suchas inner position r₁, middle position r₂, and outer position r₃respectively. The linear tilt compensation table 66 can be obtained byrecording the focus output voltages 54.

Please refer to FIG. 5. FIG. 5 is a flowchart of building the tilt dacvalues of the linear tilt compensation table 66 shown in FIG. 3. In theauto-adjusting system for an optical incident angle of the presentinvention, the linear tilt dac values recorded in the linear tiltcompensation table 66 are obtained by the following steps:

Step 500: Start.

Step 502: Select an inclination.

Step 504: Input slightly different tilt adjusting signals 56 of lineartilt dac values within a predetermined range to fine-tune the pickuphead 42 to be positioned at the corresponding inclination.

Step 506: Read the data in the recording block 52 sequentially, andcalculate the corresponding data error rate.

Step 508: Select the linear tilt dac value with the lowest data errorrate to be recorded in the linear tilt compensation table 66.

Step 510: Judge whether there is any inclination that is not completed.If yes, go to step 500, or go to step 512.

Step 512: Finish.

In other words, the method, which obtains these linear tilt dac values,is to select different inclination angles and repeat step 504 to step508 until all linear tilt dac values in the linear tilt compensationtable 66 are all recorded.

Please refer to FIG. 1 and FIG. 2. The inclination θ1 caused by the tiltof spindle 22, disc spindle 24, pickup head track spindle 26, and mirrorspindle 28 is called linear inclination. The optical informationrecording/reproducing apparatus 40 will have the ability to processthese kinds of linear inclinations by the linear tilt compensation table66.

However, with non-linear inclination caused by the tilt compact disc,the non-linear tilt compensation table 68 shown in FIG. 3 is necessary,so that the optical information recording/reproducing apparatus 40 canutilizes the controller 64 to adjust the inclination of the pickup head42.

Please refer to FIG. 6. FIG. 6 is a schematic diagram of a tilt compactdisc 51 used by the optical information recording/reproducing apparatus40 shown in FIG. 3. The tilt compact disc 51 begins to generatenon-linear deformation at the position of the second radius distance r₀away from the center. Taking the radius r shown in FIG. 6 as an example,the tilt of any radius distance between the center and r₀ is a lineartilt angle θ₂, and the tilt of any radius distance r₄ larger than r₀ isa non-linear tilt angle. The present invention obtains the non-lineartilt compensation parameters β via the following equation afterobtaining the position where the tilt compact disc 51 begins to generatesecond radius distance r₀ and cooperating with first radius distance rand linear tilt angle θ₂.

$\beta = \frac{{{SIN}^{- 1}\left( {\left( \frac{r}{r - r_{0}} \right)*{SIN}\;\theta_{2}} \right)} - \theta_{2}}{\theta_{2}}$

Wherein θ₂ is first being kept constant, the non-linear tiltcompensation parameters β in the non-linear tilt compensation table 68are obtained by changing r and r₀; θ₂ is then being changed, and theabove method is repeated to build the non-linear tilt compensation table68.

Please refer to FIG. 3, FIG. 6, and FIG. 7. FIG. 7 is a flowchart ofcomparison procedure of generating second radius distance r₀ as shown inFIG. 6. According to the predetermined comparison procedure shown inFIG. 7, the non-linear tilt calculation unit 62 shown in FIG. 3 obtainsthe second radius distance r₀ where the tilt compact disc 51 begins togenerate non-linear deformation shown in FIG. 6. The predeterminedcomparison procedure comprises the following steps:

Step 700: Start.

Step 702: Utilize the pickup head 42 to read data in a start position 55of the inner circle of the compact disc 42, obtain the correspondingfocus output voltage 54, and define the first linear tilt dac valuecalculated by the linear tilt calculation unit 60 as bTiltDAC_offset.

Step 704: Read the compact disc 50 from the inner circle to the outercircle by the pickup head 42, and obtain the corresponding focus outputvoltages in each predetermined radius position.

Step 706: Consulting the linear tilt compensation table to calculate thepresent linear tilt dac values 70 by the linear tilt calculation unit60, according to each radius position and the obtained focus outputvoltage.

Step 708: Compare the present linear tilt dac value 70 with the firstlinear tilt dac value.

Step 710: Judge whether the present new linear tilt dac value exceedsthe first linear tilt dac value by an acceptable average range. If yes,go to step 712, or go to step 704.

Step 712: Define the radius position corresponding to the linear tiltdac value as the second radius distance r₀ wherein the non-lineardeformation occurs.

Step 714: Finish.

By building the linear tilt compensation table 66 and the non-lineartilt compensation table 68, the auto-adjusting system 44 for an opticalincident angle can calculate the inclination of optical incident anglefrom the laser beam 48 to the compact disc 50.

Compared with the prior art, the optical informationrecording/reproducing apparatus 40 doesn't need to install a tiltsensor; it obtains the tilt of the optical incident angle from the laserbeam 48 to the compact disc 50 by the prior art, which utilizes thefocus output voltage 54 to keep a focus distance between the pickup head42 and the compact disc 50. After calculating and obtaining the tilt ofthe optical incident angle, the auto-adjusting system 44 for an opticalincident angle of the present invention further actuates the inclinationof the pickup head 42, so that the laser beam 48 is parallel to thenormal direction of the selected recording block 52, thus achieving theobjective of auto-adjusting for an optical incident angle. Therefore,the optical information recording/reproducing apparatus, which utilizesthe auto-adjusting system 44 for an optical incident angle of thepresent invention, not only can maintain the optical informationrecording/reproducing quality but is also acceptable under theconsideration of cost when producing the optical informationrecording/reproducing apparatus.

With the example and explanations above, the features and spirits of theinvention will be hopefully well described. Those skilled in the artwill readily observe that numerous modifications and alterations of thedevice may be made while retaining the teaching of the invention.Accordingly, the above disclosure should be construed as limited only bythe metes and bounds of the appended claims.

1. An auto-adjusting system for an optical incident angle in an opticalinformation recording/reproducing apparatus, the optical informationrecording/reproducing apparatus comprising a pickup head and a tiltactuator, the pickup head generating a laser beam to read data from arecording block of a first radius on a compact disc and receive a focusoutput voltage (FOSO) in responsive to the reflected laser beam, thetilt actuator outputting a tilt adjusting signal to correct theinclination of the pickup head, so as to keep the laser beam at apredetermined optical incident angle to read data from the compact disc,the auto-adjusting system comprising: a memory for storing a linear tiltcompensation table and a non-linear tilt compensation table, the lineartilt compensation table being built via a predetermined linear tiltadjusting procedure and comprising a plurality of focus output voltagesand a plurality of corresponding linear tilt dac values, the non-lineartilt compensation table recording a plurality of non-linear tiltcompensation parameters, each non-linear tilt compensation parameterbeing a function of the first radius and a second radius wherein thecompact disc begins to generate non-linear deformation; a linear tiltcalculation unit, for calculating the corresponding linear tilt dacvalue by consulting the linear tilt compensation table according to thefirst radius and the focus output voltage; a non-linear tilt calculationunit, for generating the second radius wherein the compact disc beginsto generate non-linear deformation according to a predeterminedcomparison procedure, and then obtaining the corresponding non-lineartilt compensation parameter by consulting the non-linear tiltcompensation table according to the first radius and the second radius;and a controller for controlling the pickup head, the memory, the lineartilt calculation unit, and the non-linear tilt calculation unit;wherein, when the pickup head reads data from the recording block on thecompact disc, the controller controls the calculation of a tiltcompensation equation by inputting the linear tilt dac value generatedby the linear tilt calculation unit and the non-linear tilt compensationparameter generated by the non-linear tilt calculation unit, and enablesthe tilt actuator to output the corresponding tilt adjusting signal tothe pickup head according to the calculation result, so as to on-lineadjust the inclination of the pickup head.
 2. The auto-adjusting systemof claim 1, wherein the pickup head comprises a laser diode forgenerating the laser beam and a photo detector for detecting the laserbeam reflected from the recording block, and the tilt actuator comprisesa digital to analog (D/A) converter for converting the calculationresult of the controller into the corresponding tilt adjusting signal toadjust the inclination of the pickup head.
 3. The auto-adjusting systemof claim 1, wherein the tilt actuator enables the laser beam generatedby the pickup head to parallel the normal direction of the selectedrecording block, so that the predetermined optical incident angle issubstantially kept at 90 degree to reduce the error rate when readingdata from the recording block.
 4. The auto-adjusting system of claim 1,wherein the optical information recording/reproducing apparatuscomprises a spindle for rotating the compact disc, and there is at leastone inclination adjusting screw accommodated on the spindle foradjusting the horizontal inclination as the compact disc rotates.
 5. Theauto-adjusting system of claim 4, wherein the linear tilt adjustingprocedure builds the linear tilt compensation table by the followingsteps: placing a normal non-tilt disk in the optical informationrecording/reproducing apparatus; adjusting the inclination adjustingscrew to enable the normal non-tilt disk to rotate under differentinclination; and recording the corresponding focus output voltages inseveral different radius positions under each inclination angle, andobtaining the corresponding linear tilt dac values to complete thelinear tilt compensation table.
 6. The auto-adjusting system of claim 5,wherein the linear tilt dac values recorded in the linear tiltcompensation table are obtained by the following steps: for a giveninclination angle, inputting slightly different tilt adjusting signalswithin a predetermined range to fine tune the pickup head to bepositioned at the corresponding inclination angle; reading the data inthe recording block sequentially, identifying the corresponding dataerror rate, and selecting the linear tilt dac value with the lowest dataerror rate to be recorded in the linear tilt compensation table; andselecting different inclination angles and repeating the above two stepsuntil all linear tilt dac values in the linear tilt compensation tableare all recorded.
 7. The auto-adjusting system of claim 1, wherein thefocus output voltages recorded in the linear tilt compensation table arethe received focus output voltages when the pickup head is positioned atan inner circle, a middle circle, and an outer circle respectively, andthe focus output voltages are obtained after filtration via a low-passfilter.
 8. The auto-adjusting system of claim 1, wherein the comparisonprocedure comprises the following steps: utilizing the pickup head toread data in a start position of the inner circle of the compact disc,obtaining the corresponding focus output voltage, and then generating afirst linear tilt dac value calculated by the linear tilt calculationunit; reading the compact disc from the inner circle to the outer circleby the pickup head, obtaining the corresponding focus output voltages indifferent radius positions, and generating the corresponding linear tiltdac values calculated by the linear tilt calculation unit at differentradius positions; and comparing the present linear tilt dac valuecalculated by the linear tilt calculation unit with the first lineartilt dac value, and if the present linear tilt dac value exceeds thefirst linear tilt dac value by an acceptable average range, defining thecorresponding radius position as the second radius wherein thenon-linear deformation occurs.
 9. The auto-adjusting system of claim 8,wherein the first radius is defined as r, the second radius is definedas r₀, the linear tilt angle of the compact disc is defined as θ₂, andthe non-linear tilt compensation parameter is defined as β and isobtained by the following equation:$\beta = \frac{{{SIN}^{- 1}\left( {\left( \frac{r}{r - r_{0}} \right)*{SIN}\;\theta_{2}} \right)} - \theta_{2}}{\theta_{2}}$wherein the non-linear tilt compensation parameters β in the non-lineartilt compensation table are obtained by fixing θ₂ and changing r and r₀.10. The auto-adjusting system of claim 9, wherein the linear tilt dacvalue calculated by the linear tilt calculation unit is defined asbLinearTiltDAC, the first linear tilt dac value obtained by the pickuphead when reading the start position of the compact disc is defined asbTiltDAC_offset, the non-linear tilt compensation parameter obtained bythe non-linear tilt calculation unit is defined as β, and the controllergenerates the calculation result defined as Theta from the followingtilt compensation equation:Theta = b LinearTiltDAC + (bLinearTiltDAC − bTiltDAC_offset) + 2 * β * (bLinearTiltDAC − bTiltDAC_offset)11. The auto-adjusting system of claim 1, wherein the controller adjuststhe inclination of the pickup head every 200 ms to 500 ms.
 12. Theauto-adjusting system of claim 1, wherein if the pickup head is notpositioned at any one predetermined radius in the non-linear tiltcompensation table, the controller calculates the corresponding lineartilt dac value by interpolation.